The invention relates to a method of manufacturing a semiconductor device, comprising the provision of a substrate with a dielectric layer on this substrate, a conductive layer on the dielectric layer, an inorganic anti-reflection coating on the conductive layer, and a resist mask on the inorganic anti-reflection coating, which method comprises the following steps:
patterning the inorganic anti-reflection coating by means of the resist mask,
patterning the conductive layer by etching down to the dielectric layer,
removing the resist mask, and
removing the inorganic anti-reflection coating.
Such a method is known from U.S. Pat. No. 5,963,841. Conductive gates are formed here in a semiconductor device through the use of a xe2x80x9cbottom anti-reflective coatingxe2x80x9d (BARC). The starting material is the substrate provided with a dielectric layer as described above, a conductive layer, a BARC provided with an oxide layer, and a resist mask. The regions of the oxide layer selected by the resist mask, the BARC, and the conductive gate layer are etched. Then the resist mask is removed so that the subjacent oxide layer becomes exposed. The oxide layer is also removed then, which exposes the BARC. Finally, the remaining BARC is removed.
It was found in the known method that a loss of the critical dimension (CD) of the gate occurs. The dimension of the passage in the conductive layer does not correspond exactly any more to the dimension defined by the resist mask. A good CD control is of major importance in view of the continuing trend towards decreased dimensions of devices within an IC. It was also found that an edge roughness arises at the area of the etched groove in the conductive material.
The invention has for its object inter alia to provide a method of the kind described in the opening paragraph in which no or substantially no changes occur in the CD.
According to the invention, the method is for this purpose characterized in that the inorganic anti-reflection coating is removed by means of a dry etch step using a polymerizing gas.
The dry etch has a good selectivity with respect to the conductive layer (which is made, for example, of polycrystalline silicon) and oxide and thus causes no change in the CD. The known method uses a wet etch step. The invention is based on the recognition that this etch has a low selectivity between the anti-reflection coating (ARC) and the conductive layer (for example polycrystalline silicon) such that a CD loss occurs owing to the isotropic character of the etch.
In an embodiment of the method according to the invention, the inorganic ARC used is silicon oxynitride (SiOxNy). The layer of conductive material comprises, for example, polycrystalline silicon, but it may also be made of alternative materials such as SiGe and metals such as Al. After etching of the layer of conductive material, the Layer of SiOxNy is removed by means of a dry etch. The dry etch preferably utilizes a polymerizing gas of type CHxFy such as, for example, CH3F. This etch has a good selectivity with respect to polycrystalline silicon and oxide. It should be noted that the values of x and y in SiOxNy need not be the same as the values of x and y in CHxFy.
In a further embodiment, an oxide layer is used on the inorganic ARC, inter alia for preventing chemical contamination of the resist mask by the ARC. The oxide layer may be obtained not only through deposition but also through a plasma treatment of the SiOxNy layer. In the latter case, a top layer arises with a thickness which is not accurately defined and which comprises more oxide than does the rest of the ARC. Since the dry etch by means of which the ARC is removed is selective with respect to oxide, the oxide present on the ARC is preferably removed before the ARC is removed in the dry etch. In a further embodiment, the resist mask is the first to be removed after the patterning of the oxide layer and the subjacent inorganic ARC by means of a resist mask. Then two steps for etching the polycrystalline silicon are carried out. First the oxide layer is removed in a known manner by means of an etch. It is possible that part of the SiOxNy layer is etched at the same time during this if the etching process does not stop in time. Then the remaining portion of the SiOxNy layer is used as a hard mask for etching the polycrystalline silicon in a known manner. The high selectivity of the polycrystalline silicon etch with respect to SiOxNy achieves that the mask is not attacked. Finally, the remaining portion of the mask is removed in the dry etch step.
An additional advantage of the latter embodiment is that the inorganic hard mask by means of which the polycrystalline silicon is etched does not influence the etching chemistry. In U.S. Pat. No. 5,963,841, the polycrystalline silicon is etched by means of the organic resist mask, which does participate actively in the chemistry during the etching treatment and accordingly influences the final result.
Another advantage is that attacks on the dielectric layer situated under the polycrystalline silicon are prevented through the removal of the oxide layer before the polycrystalline silicon is etched. This dielectric layer consists, for example, of oxide (the so-called gate oxide). If this gate oxide is exposed already at the moment when the oxide layer is removed from the ARC, the etching treatment in which this removal is effected will also attack the gate oxide and the insulation.